The present invention relates to a defect inspection method, defect inspection apparatus, and defect inspection system used to inspect and observe defects, foreign particles, and the like, on the micropatterns formed on substrates through a thin-film forming process represented by manufacturing processes for semiconductors and/or flat-panel displays.
Fine-structuring of the patterns formed with photolithography is progressing with the enhancement of semiconductor integration density and the improvement of flat-panel display resolution. During the manufacturing processes for these products, the formation of the patterns is followed by defect inspection and/or the like in order to improve production yields. During the defect inspection, the patterns are detected as images by an optical system and then defects are extracted by comparing these images with those of adjacent dies (or cells). When it comes to the generation of sub-100 nm in terms of pattern size, however, optical systems lack resolution and pattern images become difficult to accurately detect. In the field of defect inspection optical systems, therefore, the resolution enhancement technology described in Japanese Patent Laid-Open No. 2000-155099 (corresponding to U.S. application Ser. No. 09/397,334) is known as an ultrahigh-resolution detection technology that uses wavelength reduction, numerical aperture (NA) enhancement, and light polarization.
In response to fine-structuring of technical nodes, wavelength reduction and NA enhancement are also progressing in the field of lithography. At present, the exposure apparatus that uses ArF laser light of a 193 nm wavelength is in practical use, and for further reduction in wavelength, F2 laser light with a wavelength of 157 nm is expected as a promising light source. However, the exposure with F2 laser light, presents problems such as increases in apparatus costs because the construction of an optical system becomes complex and decreases in exposure margins due to decreases in the depth of focus during exposure. For this reason, WO Patent Publication No. WO99/49504 describes the exposure technology that achieves the improvement of resolution and the suppression of decreases in exposure margins at the same time by applying the liquid immersion exposure that uses, for example, ArF laser light as exposure light.
In the above ultrahigh-resolution detection technology that uses light polarization, when a sample is irradiated with specific polarized light via a dry-system objective lens by incident illumination, the light thus reflected/diffracted is captured by the same objective lens and an image of the sample is detected using an image sensor. This conventional technology has had the characteristic that an optical image of the sample can be obtained with high contrast by detecting this image using only specific polarized components of the reflected/diffracted light. However, in a sample, represented by a semiconductor wafer, that has undergone a thin-film forming process, a transparent film made of silicon dioxide (SiO2), for example, is formed as an interlayer-insulating film. This insulating film has thickness unevenness in the wafer. During the inspection, such film thickness unevenness should originally not be detected since it has no fatal influence on device characteristics. During observation through a dry-system lens, however, thin-film interference on the transparent film causes the unevenness of the film thickness to appear as the unevenness of brightness on the image detected. For example, during comparative inspection with respect to adjacent dies, if the transparent films on these adjacent dies are uneven in film thickness, differences in the brightness of the respective images detected will occur and an image of the object will be incorrectly detected as a defect image. Increasing an inspection threshold value in an attempt to avoid such incorrect detection will pose the problem that total inspection sensitivity decreases.
Also, etched patterns are usually subjected to defect inspection. During defect inspection, therefore, sufficient consideration must be given to the fact that the pattern materials varying in type and form and in surface roughness (surface irregularities in level) are used in semiconductor processes.